Multicast in MPLS/BGP IP VPNs

[Chatschik Bisdikian <bisdik at us.ibm.com>]

Dear members of the l3vpn distribution
list,

The draft-ietf-l3vpn-2547bis-mcast-00.txt
(May 2005) presents a new framework and terminology to support multicasting
over provider-provisioned BGP/MPLS VPNs. The framework encompasses under
a common umbrella several options for MVPN control plane, data plane and
other relevant functions (many of these choices have been considered on
their own right in previous drafts).

This note  focuses on PE-PE transmission
of multicast routing described in section 5 of the "2547bis-mcast"
draft. We believe that to achieve productive progress and increase interoperability
chances among products from different vendors that will support 2547bis-based
MVPNs, the number of alternatives in section 5 need to:

a) Be reduced to a minimum number of
possible alternatives, and
b) Clearly spell out required and optional alternatives.

Among the alternatives, we believe that
BGP is the preferred approach. BGP has the advantage of:

- reliable transport;
- established inter-provider operations;
- a parallel operational model of the
unicast 2547.

The above *non-exhaustive* list provides
benefits both in technical terms (reliability) and in operational terms
(exploiting/leveraging established operational familiarity with the unicast
2547 case).  Using the PIM alternatives in section 5, both multicast
or unicast, does not provide any of these advantages -- section 5.1 (PIM
peering) points out that the periodic refresh of PIM C-Join/Prune messages
(which is done to provide a level of reliability for PIM) disadvantages
the PE routers.

We therefore propose to elect BGP as the required way to carry multicast
routing information between PEs as described in section 5.2 of the draft
and, at a minimum, we propose the elimination of section 5.1.3 (Unicasting
of PIM C-Join/Prune messages).

Regards,

Chatschik Bisdikian 
IBM T. J. Watson Research Center

John E. Drake
Boeing Satellite Systems